Ignition device for internal combustion engine

ABSTRACT

A CHANGE OF PREDETERMINED POLARITY ACCUMULATED ON A CAPACITOR BY A DC SOURCE DISCHARGES IN OSCILLATORY MODE INTO AN IGNITION COIL THROUGH A THYRISTOR GATED AT EACH IGNITION TIME OF THE ASSOCIATED ENGINE FOR IGNITION PURPOSE. IN THE DISCHARGE, A VOLTAGE SUCCEEDINGLY APPEARING ACROSS THE CAPACITOR OF A LOWER MAGNITUDE WITH OPPOSITE POLARITY CAUSES A VOLTAGE DROP ACROSS A DIODE AND A VOLTAGE DROPPER SUCH AS AN INDUCTANCE OR A ZENER DIODE SERIALLY CONNECTED ACROSS THE THYRISTOR TO RENDER IT NONCONDUCTING. THE THYRISTOR IS NOW READY FOR THE SUCCEEDING IGNITION OPERATION AND THE CAPACITOR IS AGAIN CHANGED BY THE SOURCE. FOR A MULTIPLE-CYLINDER ENGINE, EACH IGNITION PLUG INVOLVED IS ASSOCIATED WITH THE INDIVIDUAL IGNITION COIL, THYRISTOR AND DIODE WHILE THE CAPACITOR AND THE VOLTAGE DROPPER ARE USED IN COMMON WITH ALL THE PLUGS.

Jan. 5, 1971 TAKAQ Mm] 3,553,725

IGNITION DEVICE FOR INTERNAL coNEus IoN ENGINE Filed Nov. 27, 1968 FROM 20 F/GQZ a 23 United States Pat 3,553,725 Patented Jan. 5, 1971 ABSTRACT OF THE DISCLOSURE A change of predetermined polarity accumulated on a capacitor by a DC source discharges in oscillatory mode into an ignition coil through a thyristor gated at each ignition time of the'associated engine for ignition purpose. In the discharge, a voltage succeedingly appearing across the capacitor of a lower magnitude with opposite polarity causes a voltage drop across a diode and a voltage dropper such as an inductance or a Zener diode serially connected across the thyristor to render it nonconducting. The thyristor is now ready for the succeeding ignition operation and the capacitor is again charged by the source. For a multiple-cylinder engine, each ignition plug involved is associated with the individual ignition coil, thyristor and diode while the capacitor and the voltage dropper are used in common with all the plugs.

BACKGROUND OF THE INVENTION This invention relates in general to an ignition device for use with an internal combustion engine, and more particularly to a capacitor discharge type ignition device wherein a charge accumulated on acapacitor involved is discharged into the associated ignition coil, through a thyristor connected thereto at each ignition time of the associated internal combustion engine for ignition purpose. H

The conventional type of ignition devices referred to has comprised a capacitor connected to a source of direct current to be charged with a DC voltage from the source, an ignition coil of the Well-known construction including a primary and a secondary winding, and a thyristor or a semiconductor controlled rectifier connected in a circuit for discharging a charge accumulated on the capacitor into the primary ignition winding. The capacitor is maintained fully charged with a DC voltage of a predetermined polarity from the source while at each time point at which the associatedinternal combustion engine is to be ignited a gating signal is supplied to the gate electrode of the thyristor. This causes the thyristor to be gated to permit the charge on the capacitor to be discharged into the primary ignition winding through the now conducting thyristor whereupon an ignition voltage is induced across the secondary ignition winding to strike a spark across a spark gap in the associated ignition plug.

It is desirable to increase a discharge energy appearing on the ignition plug to ensuring the ignition of a fuel contained in the associated combustion chamber while the fuel is completely burnt out. To this end, it is required that even after the particular electric discharge has been initiated across the spark gap in the ignition plug, another voltage should be further applied across the ignition spark to sustain the discharge. In the conventional ignition device as above described, therefore, a discharge circuit including the capacitor, the ignition coil and the thyristor is oscillatory and the capacitor has developed thereacross a voltage of alternate polarity decayed during the period of discharge. Specifically, immediately after a voltage of predetermined polarity across the capaci'tor stem ming from the source has been first dis charged into the ignition coil, through the gated thyristor,

the capacitor has developedthereacross a voltage of opposite polarity which is, in turn, in the reverse direction With respect to the thyristor. Accordingly a bypass circuit 7 has been disposed around the thyristor to permit the voltage of opposite polarity to 'be appliedto the ignition coil therethrough thereby to apply to the ignition plug a voltage for sustaining the particular electric discharge thereon.

Such a bypass circuit disposed around the thyristor should not bypass the latter for the initial voltage of predetermined polarity across the capacitor originating from the source. However for the succeeding voltage of opposite polarity. developed across the capacitor during the period of discharge, the bypass circuit should benot fully but only partially short circuitthe thyristor to such an extent that a voltage drop is developed thereacross sufficient to supply to the thyristor a reverse voltage for rendering it non-conducting.

If the requirements just described are met the ignition coil can provide a sustained ignition voltage to increase an electrical energy discharged on the ignition plug while ensuring that after the completion of the particular ignition operation, the thyristor is brought into its non-conducting state leading to the readiness for the succeeding ignition operation. However, the conventional bypass circuits could not meet the second requirement.

SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide a new and improved ignition device for use with an internal combustion engine capable of developing a sustained ignition voltage across an ignition coil involved to increase an electrical energy discharged across the associated ignition plug while ensuring that after the completion of the particular ignition operation the associated thyristor is rendered nonconducting ready for the succeeding ignition operation.

It is another object of the invention to provide a new and improved ignition device of the type described in the preceding paragraph, simple in construction and suitable for use with a multiple-cylinder internal combustion engine.

According to the principles of the invention, there is provided an ignition device for use with an internal combustion engine comprising a capacitor charged with a DC voltage of predetermined polarity supplied by a source of direct current, a thyristor capable of being gated at each ignition time of the engine to permit the charged voltage across the capacitor to be discharged in oscillatory mode into an ignition coil therethrough to effect an electric discharge on an ignition plug connected to the ignition coil, and a semiconductor diode and a voltage dropping element serially-connected across the thyristor. A voltage of opposite polarity developed across the capacitor immediately after the charged voltage across the capacitor has been first discharged into the ignition coil causes a voltage drop across the serially connected voltage dropping element and diode ensuring that the thyristor is rendered non-conducting.

single v oltage" dropping element is connected to all FIG. 2is a fragm'ental, schematic. circuit diagram of a modification of the invention; w r

' FIG. 3 is "a 'view similar to FIG. 2'but illustrating another modificationof the invention;

-FIG.".4 is a schematic circuit diagram, of a further modification of "the: invention suitable for use with a multiple-cylinder internal combustion engine; and

FIG. 5 is a fragmental, schematic circuit diagram. of amodificatio'ri'of the device showninFIG. 4.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS While the invention is applicable to a variety of internal combustion engines it is particularly suitable for use with internal combustion engines equipped on motor vehicles. Therefore the invention will now be described in terms'of an internal combustion engine equipped on a motor vehicle.

Referring now to the drawing and FIG. 1 in particular, it is seen that an arrangement disclosed herein comprises a source of electrical energy generally designated by the reference numeral and including an alternating current output winding 12 of a magneto driven by the associated internal combustion engine (not shown) and a semiconductor rectifier 14 for rectifying an altemating current output from the winding 12 provide a unidirectional voltage with winding 12 connected to a point of reference potentional, in this case, a vehicles chassis denoted by the symbol grounding. It is to be understood that the combination of the winding and rectifier 12 and 14 respectively may be replaced by any suitable source of direct current such as an accumulator disposed on a motor vehicle. A capacitor 16 is connected across the source 10 to be charged with a voltage of predetermined polarity from the source. Only for the purpose of illustration the capacitor 16 is shown as being charged so as to have its upper pole as viewed in FIG. 1, positive with respect to its lower pole.

The capacitor 16 is electrically coupled to an ignition coil 18 including a primary winding 20 and a secondary winding 22. Both the windings 20 and 22 are connected at one end to the upper pole of the capacitor 16 While the primary winding 20 is connected at the other end to a semiconductor controlled rectifier or a thyristor 24 and the secondary winding 22 is connected at the other end to an ignition p1ug'26 within a combustion chamber of the associated internal combustion engine connected to 'the point of reference potential. The thyristor 24 includes an anode electrode a connected-to the primary winding 20, a cathode electrode c connected to the point of reference potential and a gate electrode g adapted to be periodically energized by a pulse generator (not shown). The pulse generator is of the conventional construction and operative to generate ignition pulses with a very short duration in synchronization with the rotational movement of the associated engine (not shown) to render the gate electrode g to positive with respect to the cathode electrode 0 of the thyristor 24 to gate it at each time point when theengine is to-be ignited. It will be appreciated that the primary ignition winding 20 and the gated thyristor 24 forms a discharge circuit for discharging the'capacitor 16 charged with the polarity illustrated. p

' The junction-of the primary ignition winding 20 and the anode electrode a of the thyristor 24 is connected follows:

to a cathode electrode c of a semiconductor diode 30 whose ailo'de ele'ctrod'e a is connected 'to'the' point of reference potential through a voltage dropping element represented by a block 32 'in FlG. 1. The series combination of the diode and voltage dropping elements 30 and 32 respectively forms a bypass circuit around the thyristor 24 generally designated by the reference numeral 34. This bypass circuit 34 along the primary ignition Winding 20 forms another dischargecircuit permitting the capacitor 16 to be discharged provided that the capacitor has its polarity opposite to that illustrated. This is because the diode 30 is opposite in polarity to the thyristor 24. r

The arrangement thus far described is operated as It is now assumed that the source 10 has charged the capacitor 16 with a predetermined polarity as illustrated in FIG. 1. That is the not-grounded pole or upper pole as viewed in FIG. 1 is maintained positive with respect to the other pole thereof. Under the assumed condition; the application of a positive ignition to the gate electrode g of the thyristor 24 causes the latter to be gated with a very low voltage drop across the anode and cathode electrodes thereof. This permits a charge on the capacitor 16 to be injected into the primary ignition Winding 20 whereupon the secondary winding 22 induces thereacross a high voltage sufiicient to cause an electric discharge across the spark gap of the ignition plug 26. Thus the electric discharge is initiated on the ignition plug 26 to ignite a fuel around the plug leading to the initiation of a combustion of the fuel.

Since the discharge circuit 32 is designed and arranged to oscillate the discharge of the capacitor 16 is accompanied by a voltage succeding appearing across the capacitor with a polarity reversed from that illustrated in FIG. 1. The voltage now developed across the capacitor 16 acts as a reverse voltage for the thyristor 24 while it acts as a forward voltage for the diode 30. Therefore the polarity reversed voltage across the capacitor 16 causes a discharge current to flow from the lower or ground pole of the capacitor 16 through the voltage dropping element 32, the diode 30 and the primary ignition winding 20 and back to the upper pole of the capacitor whereby the secondary ignition winding 22 produces a voltage sufficient to sustain the particular electric discharge across the spark gap of the ignition plug 26 initially developed through from the preceding electric discharge. This leads to the more complete com- 7 bustion of the fuel to increase the resulting combustion energy and the therefore output from the engine.

The current flowing from the voltage dropping element 32 toward the primary ignition winding 20 also causes a voltage drop across the element 32 and the diode 30 serving to render the cathode electrode 0 of the thyris' tor 24 positive with respect to the anode electrode a thereof. That is, a reverse voltage is applied to the thyris tor 24. In this connection it is to be noted that the voltage dropping element 32 has a magnitude preselected so as to provide a voltage drop suflicient to render the thyristor 24 non-conducting. Therefore the above-mentioned flow of current through the element 32 causes the thyristor 24 to be brought into its open state. At that time the ignition signal previously applied to the gate electrode g of the thyristor 24 has already disappeared.

' On the other hand, the discharge circuit 28 is in its oscillatory mode of operation and a voltage with a polarity equal to that illustrated will be again developed across the capacitor 16 after the termination of the last-mentioned flow of current. However as the electric discharges occurring across the ignition plug 26 have already consumed an appreciable portion of the oscillatory energy stored in the discharging circuit, the voltage now developedacross the capacitor 16 is of a small magnitude-as compared with the particular voltage to which capacitor 16 was initially charged by the source 10. Under these circumstances if the voltage across the capacitor 16 would have"beenl'restoredrto its originalpolarity.=equal to that illustrated; theirsam'e is. not: enabled to cause anelectric dischargeracross the: ignition plug'-26;for the reasons that the thyristor 24 was already renderednon-conducting and is maintained in its open state while the diode 30 blocks a flow of current resu'ltingfrom"such a voltage. Therefore the capacitor lfi isagain charged to a higher voltage determined by the source 1Q while theoscillation of the discharging circuit decays; the thyristor is lrje'adyj for the succeedingignition operation." In this" way, the process as above described i s repea ted at each ignition time point of the associated engine to ignite it with the result that the engine is put in operation. I

The voltage dropping element as previously described may be preferably an=inductance32a a'sshown iif'FIG. 2 or a Zener diode 32b as shown in FIG. 3. In other respects, the arrangement as illustrated in FIG. 2 or 3 is identical to that shown in FIG. 1 and the same reference numerals designate the components identical to those shown in FIG. 1.

The Zener diode 32b is shown in FIG. 3 as including an anode electrode a connected to the anode electrode a of the semiconductor diode 30 and a cathode electrode c connected to the point of reference potential. Thus the Zener diode 32b presents the Zener characteristic to a voltage that renders the cathode electrode c positive with respect to the anode electrode a. When a voltage across the associated capacitor such as the capacitor .16 shown in FIG. 1 is discharged to change in polarity as previously described in conjunction with FIG. 1, bypasscircuit 34 including the Zener diode 32b and the diode 30 bypasses a thyristor 24 with a sum of the Zener voltage E of the Zener diode 32b plus the forward voltage E of the diode 30 developed across the same. Thus the arrangement exhibits the substantially same eifects as does the arrangement of FIG. 1.

The invention also contemplates to provide an ignition device suitable for use with more than one of ignition plugs such as, for example, a two-cylinder engine. FIG. 4 shows one form of the invention applied to a two-cylinder engine wherein one discharge circuit and one bypass circuit as previously described are operatively coupled to each ignition plug except for a voltage dropping element such as the element 32 being used in common to all the bypass circuit. The components as illustrated in FIG. 4 are designated by the same reference numerals denoting the corresponding components as shown in FIG. 1 and the components separately coupled to each ignition plug are designated by the corresponding reference numerals suffixed with a reference character A or B. For example, a single capacitor 16 is adapted to supply a discharge energy to each ignition plug 26A or 26B, and a thyristor 24A is operatively coupled to the ignition plug 26A. However a single voltage dropping element shown as an inductance 32B is connected to both a diode 30A and a diode 30B. By comparing FIG. 4 with FIG. 2 it will be readily appreciated that the arrangement as shown in FIG. 4 is identical in operation and results to that illustrated in FIG. 1.

As in FIG. 3, the voltage dropping element may be Zener diode 32b as shown in FIG. whereinthe same reference numerals designate the components corresponding to those shown in FIG. 4.

Similarly the invention is equally applicableto more than two ignition plugs or multiple-cylinder engines. For example, with a four cylinder engine, a single capacitor such as capacitor 16 may be operatively associated with four discharge circuits each including an ignition coil and a thyristor with one bypass circuit connected to each thyristor. However it is noted that a single volt-age dropping element is disposed in common to all the bypass circuits. Alternatively a pair of capacitors may be operatively coupled to four discharge circuits one for each pair of the circuits such as shown in FIG. 4 or 5. Under these circumstances a pair of voltage dropping elements are included in our b circuits. w

While the rmvennon vhas been illustrated and described in conjunction}; with. severalipreferred embodiments thereof itylis to belunder'stood'that numerouscha'nges, modificat'ions; and 's'ubstitution'slmay: beUIe'stQred 'to' without departing from the .spirit arid-scope ofthe invention.

What is claimed is: 3 c v "fLlAnyignition devicewforuse withilan internal combustion-engine, comprising-in combination,

(a)-a 'source of direct current rfl" I (b) a capacitor charged by said sourcey '(c) an ignition plug, 9 t 1 j :(d anrignition I coil including a primary winding conrnected to said cap'acitorand a s'econdary winding connected tosaid ignition'plug,

3 '(e). a thyristor connected to said primary winding of said ignition coil for gated conduction to discharge said capacitor through said primary winding, and

(f) a bypass circuit connected in series circuit relationship to said primary winding and in parallel circuit relationship to said thyristor, and including a semiconductor diode and Zener diode serially connected to said semiconductor diode in opposing polarity, said semiconductor diode being connected in opposite polarity to said thyristor, said Zener diode responding to a flow of forward current through said semiconductor diode to limit a voltage drop across said thyristor while providing a low impedance to current flow through said semiconductor diode to render said thyristor non-conducting and to provide a low impedance path for current to said primary winding in the direction of current flow opposite to that of said thyristor.

2. An ignition device for use with an internal combustion enging comprising, in combination,

(a) a source of direct current,

(-b) a capacitor charged by said source,

(c) a plurality of ignition plugs,

(d) an ignition coil for each of said ignition plugs including a primary winding connected to said capacitor and a secondary winding connected to the associated ignition plugs,

(e) one thyristor for each of said ignition plugs connected to said primary winding of said ignition coil to be forwardly applied with a voltage having a polarity with which said source charges said capacitor, said thyristor being capable of being gated at each time point at which the engine is to be ignited to permit a charge on said capacitor to be discharged under oscillatory mode into said primary winding therethrough,

(f) one bypass circuit for each of said ignition plugs connected in series circuit relationship to said primary winding and in parallel circuit relationship to said thyristor, and including a semiconductor diode opposite in polarity to said thyristor, and

(g) a voltage droping element serially connected to all said semiconductor diodes to respond to a flow of forward current through said semiconductor diode to provide a voltage drop thereacross, which, in turn, cumulatively cooperates with a forward voltage drop across said diode to supply the thyristor a voltage sufiicient to render it non-conducting.

3. An ignition device as claimed in claim 2 wherein said voltage dropping element is an inductance.

4. An ignition device as claimed in claim 2 wherein said voltage dropping element is a Zener diode responding to a flow of forward current through said semiconductor diode to exhibit the Zener characteristic.

5. An ignition device for use with an internal combustion engine comprising, in combination,

(a) a source of direct current,

(b) a capacitor charged by said source,

(c) a plurality of ignition plugs,

516d): afpl urality 10f ignition.cojlsleach iincluding iazfpri: a' lowuimpedairce 'to current flow therethroughr'to mary winding connected to said capacitor, rand-a :p'rovide alow-:ifnpedancemath forcur'reritatosaid isecondary (winding; said 826011621131"'.-Windings,"'COnrim r wi difi j di ctid -of u r pfl .s.-"nectedwrspectiylyrtoisaidaignition-lplugs;-- .z' positeaato thatofsaid'thyristors f --:.(e)'-rmpluralityi:ofathyristors connectedarespectively to saidprimary-win'dings ofg said ignitiomcoils for gated conduction iito discharge -sai'd capactior: through said;

primary windings, a tar: 25 1(f Ja plurality;of;bypasscircuits:Jconnected"respectively in series circuitirelationship'to said primary 'winm 10 ings, and in parallel. circuitrelationship to .said thyristors, andzceach 'lincludirtgassemicondpctor diode it a; 1 connected in opposite polarity to'saidithyri'stor, and a Us X R v xZenen;diodeserially;connected incopposingcpolarity 5 with said-semiconductor;diodeto respond to aflow of 3 -1 5 5* forward current th ough .Isaid fsemicondnctor diode to a Y to .provideadvoltage drop! therea-cross while providing 

